Is it obligatory to buy an apartment in a modest neighborhood to avoid the envy and malice of the husband's brother, or to live freely as long as it does not displease Allah, and how should the husband deal with his exploitative brother?

If the husband is able to purchase a good dwelling and fine furniture without extravagance, then his fear of his brother's envy should not prevent him. He must fortify himself with remembrances (dhikr) and rely on Allah. It is permissible for him to demand his financial rights from his brother, while maintaining kinship ties with him and not severing them. Maintaining ties with a resentful brother and showing kindness to him is among the best acts of righteousness and extinguishes malice and envy. Furthermore, maintaining kinship ties is a cause for blessings in sustenance and lifespan.